Yes, this is usually normal, and it happens for a few different reasons at once. Solar panels do not respond to shade in a gentle, linear way. Even a small shadow across part of a panel can cut output a lot more than people expect, because the shaded cells start limiting the current for the whole panel. If your panel is made of multiple strings of cells, one shaded section can drag down the performance of the entire array. That is why the drop can look dramatic even when only part of the panel is shaded.
The other big factor is that solar generators are only as fast as the power they receive. If the panel is producing less voltage or current in shade, the charging electronics have less usable power to work with. Most portable power stations and their built-in charge controllers will simply accept what the panel can provide, so the battery charges more slowly. If the sunlight is weak or filtered through trees, clouds, or a balcony railing, you may also be below the panel’s ideal operating point, which further reduces charging speed.
Temperature, cable length, and connector quality can make it worse too. A long thin cable can waste power, especially when the panel is already underperforming in shade. Loose or dirty connectors can add resistance and reduce the power reaching the unit. If your setup has a low-voltage panel and the generator needs a minimum input voltage to start charging efficiently, partial shade can push it close to that threshold and cause very slow or inconsistent charging.
What usually helps is moving the panel so it gets direct sun for most of the day, even if that means changing its angle a few times. Try to keep shadows off the panel completely, because half-shade is often almost as bad as full shade from a charging standpoint. If you have the option, use more than one panel and wire them in a way that matches your power station’s input range. Some people also get better results with panels that have bypass diodes and with MPPT-based charge controllers, since those handle changing light conditions better than basic systems.
If you want to troubleshoot your setup, compare charging speed in full sun versus shade and watch the input watts or amps on the display. If the numbers fall sharply in shade, nothing is likely broken. If the drop seems extreme even in good sun, then it may be worth checking panel cleanliness, cable size, connector tightness, and whether the panel voltage actually matches what your generator wants.
